141 Fall 2019 Week 9

This week, we review a little and also study the final topic: How torque is the rate of change of angular momentum, and how they are both vectors, so when torque is perpendicular to angular momentum, torque doesn’t increase or decrease angular momentum. Instead, torque causes the angular momentum to change direction. This is precession.

Monday Be ready to finish your projects. We look at angular momentum as stability.

Before Class

During Class

  • Why must we spin frisbees or footballs to make them fly stable?
  • Precession – what is it?


Before Class

  • If you’re interested in more of this kind of learning, please consider taking one of my other classes: Energy, Society, and the Environment (PSc 320, winter quarter), Appropriate Technology Classes (PSc 391 in Fall, PSc 392 Spring – 391 is not a prerequisite for 392)
  • Please take this short Survey #9
  • Here is a precession video I made recently to explain precession.
  • read 7.5 in your text about precession.
  • See Veritassium video on how angular momentum provides increased stability against rotation. See if you can apply the explanations from our previous gyroscopic stabilization video.
  • Group project is due next weekend, Midnight Saturday night before last week of classes. 

In Class

  • What is precession?
  • Assessment #9

After Class


  • FREE FLU SHOTS at Kennedy library, 10-2, Thursday, tomorrow. Although we already know they are always free for students at the health center!
  • Please see Precession by Veritassium that explains things a little differently than I did in our previous video. Please reflect if there is something new to learn. Do we need to see both videos?
  • See work on an inclined plane video.  
  • Please look over these activities on Gyroscope Worksheet. Can you try some of them at home?
  • Solutions to PS#9 posted on main class website.

During Class

  • We will execute these activities on Gyroscope Worksheet (link above).
  • What is counter steering on a motorcycle?

Thursday: Why do kids learning how to ride a bike run into things like trees? – countersteering
Before Class

  • Hey, so you saw the video  about gyroscopic stabilization. THEN we did our activity. NOW, please see this video about countersteering (a bicycle or motorcycle).
  • Read up a little on counter steering on Wikipedia.
  • Hey, so having covered precession and gyroscopic stabilization, we’ve completed the conceptual content of the class! OMG, we’re done? The rest of the class is about review and increased examples. So, dig in! Learn what you might be weak on… prepare for the final exam.
  • Read 7.6 on two irrelevant equations and trigonometry that you are allowed to use now.
  • See Trigonometry Video , now you’re allowed to use trigonometry, but remember you can also always draw a picture if you’re not sure.
  • See 1D, 2D Kinematics Video and then you’re allowed to use those two unnecessary (in my opinion) equations, although hopefully, you’ve realized by now that you can get along without them just fine.
  • Optional: Here is an old precession video I made a few years ago. It’s long and slow with lousy graphics, but it has well over 3000 views, so some people found it helpful: Pete’s OLD Precession Video .

During Class

  • finding coefficient of friction

After Class
Send me your video link as soon as you can! The sooner I see your video, the sooner I can give you feedback.

Please send me:
1) Title of Video
2) Full Name of each person in the group.
3) Description of the project.
4) The url of the video you just posted. Please make sure that the video is public so I can see it.